1. Field of the Invention
The present invention relates to a vibration actuator including a vibration element and a relative moving member which operate as a multiple degrees of freedom type of drive device, and, more particularly, the present invention relates to a vibration actuator which is capable of generating motion around at least two axes with a frame shaped vibration element having a plurality of drive force output members.
2. Description of the Related Art
Rotary type drive devices are known, such as low torque electric motors, which generate high speed rotation to produce a drive force which is output to a driven object via a gear train speed reduction mechanism. However, the conventional rotary type drive devices are bulky and heavy, and have a complicated structure. Further, the speed reduction mechanism of the conventional rotary drive device includes plural gear wheels which generate substantial mechanical noise. Furthermore, play, inertia and the like arise between the gear wheels in the conventional rotary type drive device, resulting in poor accuracy of position determination and responsiveness.
Moreover, a multiple degrees of freedom rotary type drive device is known which generates rotary motion in independent multiple directions (i.e., in a three dimensional X-Y-Z coordinate system, a direction around the X-axis, a direction around the Y-axis, and direction around the Z-axis). However, the multiple degrees of freedom rotary type drive device requires complex transmission mechanisms resulting in increased size, weight, complexity and noisiness of the device.
To eliminate the complex transmission mechanisms of the conventional rotary type drive device, multiple degrees of freedom vibration actuators have been proposed which are small in size and produce a high torque. FIG. 33 is a diagram showing an example of a prior art multiple degrees of freedom type vibration actuator.
As shown in FIG. 33, the known vibration actuator 200 includes a spherical rotor 201 and four annular stators 202a, 202b, 202c and 202d which support the rotor 201. Piezoelectric elements (not shown in the drawing) are adhered to each stator 202a-202d on the side facing the rotor 201. The piezoelectric elements are spatially polarized so as to produce cosine components and sine components in each half cycle of an alternating voltage impressed on the piezoelectric element. More specifically, by respectively impressing two high frequency voltages in the ultrasonic region on the piezoelectric elements, a time and phase advancing traveling wave is excited in the stators 202a-202d. A force which rotates the rotor 201 is transmitted from the stators 202a-202d to the rotor 201 by the contact between the wave front of the traveling wave and the contact portion of the rotor 201. Motion having two degrees of freedom is produced by the vibration actuator 200 shown in FIG. 33 in the two sets of mutually opposite stators 202a, 202b and 202c, 202d by the input of the same drive signal. The drive force of the vibration actuator 200 is output by the oscillating motion of an output member 203.
The prior art vibration actuator shown in FIG. 33 is small in size in comparison with a rotary drive device in which an electromagnetic motor is used. However, because four stators 202a-202d are necessary, a sufficiently small in size and light weight vibration actuator can not be achieved by the vibration actuator shown in FIG. 33. Moreover, the motion of the rotor 201 obtained with the prior art vibration actuator 200 has only two degrees of freedom, and motion around the Z-axis is not possible. Therefore, the number of applications and the types of application of the prior art vibration actuator 200 are limited.
Further, the four stators 202a-202d are affixed to the rotor 201. As a result, the rotating portion of the vibration actuator 200 becomes heavy and its inertia becomes large, resulting in large losses of drive efficiency. Still further, a drive force from the vibration actuator 200 shown in FIG. 33 is output only by the oscillating motion of an output member 203 which protrudes from an exterior surface of the rotor 201. Thus, the output can only be transmitted to a driven object by directly coupling the rotor 201 to the driven object.